Water Usage

The total water makeup rate (WMR) requirement for a cooling tower is the sum of losses from evaporation (E), blowdown (B), and drift (D), a term that refers to liquid droplets entrained in the exhaust air stream. All of the lost and removed water must be replenished with fresh makeup water.

Using 1,000 Btu/lbm (0.646 kWhh/kg) as the amount of heat absorbed in the evaporation of water, evaporation rate, in gpm, can be calculated as:

In SI units, the evaporation rate, in lpm, would be:

(Tons x Btu heat rejection per ton) (1,000 Btu/lbm x 8.34 Ibm/gal x 60 min/hr)

If, for example, the heat rejection is 15,000 Btu/ton-h (1.25 kWhh/kWhr), the evaporation rate for a 4,000 ton (14,064 kW) system is:

(1,000 Btu/lbm x 8.34 Ibm/gal x 60 min/hr) = 120 gpm (454 lpm)

If the actual load is not known, the evaporation rate can be approximated based on the condenser water flow rate and temperature differential. A commonly used formula for estimating the evaporation rate, in English units, is:

Dissolved and suspended solids entering the system are not removed in the process of evaporation; therefore, the concentration of these impurities can rapidly increase in operating cooling towers. Blowdown requirements for a given system are based on maintaining the concentration of contaminants below maximum acceptable levels. The ratio of allowable concentration of impurities to the concentration existing in entering makeup water is referred to as cycles of concentration (C). Excluding consideration of drift, required blowdown rates can be determined by the following formula:

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

Get My Free Ebook

Post a comment